Sawing and Patterning

Decorative cuts and sandblasted patterns achieved with stencils can enhance the appearance of stained surfaces. Timing of these operations, though, depends on the desired effect. When you want the overall stain finish to be as evenly colored as possible, cut lines and patterns after staining is complete. Stains penetrate differently around indentations. If there is to be a color change at a pattern line, cut the line first to form a barrier to stain movement. If sawed joints are to be grouted, complete the staining and sealing before grouting to help prevent grout accumulation on the unprotected stain.

Pattern lines are generally laid out with pencil or chalk. Mark only where you cut, and don’t use chalk colors that are difficult to remove, or adhere lines to the concrete surface using clear fixative sprays. Many tools are available for cutting pattern lines in concrete. Most installers use grinders or hand-held saws with tables that ride against guides. Dry-cutting diamond blades that do minimum damage to the edge of the cut are a good choice. Dust-collection devices that attach to grinders and saws capture almost all of the dust. A 1 1 /2 -inch extruded aluminum "L" angle, available in most hardware stores, makes a good saw guide.
If you cut patterns before staining, cut them just before cleaning the surface in preparation for the stain. Sawing dust contains free lime that can adhere to the surface, causing color distortion. If you cut after staining, do it after the first coat of sealer has been applied.

Dramatic effects also can be achieved by applying stencils to surfaces after staining and then sandblasting to reveal plain or colored concrete in areas not covered by the stencils. These stencils are usually made from plastic materials and have adhesive backings that stick to the floor surface. One coat of sealer is recommended before sandblasting to improve stencil adhesion.

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